French marine archaeologists have uncovered a massive submerged wall off the Brittany coast, estimated to date back to around 5,000 BC.
They suspect it may have been built by a Stone Age community whose disappearance beneath rising waters could have inspired an old local legend about a drowned city.
Researchers think it might have served as a protective barrier against encroaching tides or functioned as a large-scale fish trap.
When it was originally constructed on the Ile de Sein at the far western edge of Brittany, the wall would have sat along the shoreline, somewhere between the high and low tide zones.
Today, the entire formation lies beneath nine meters of water, as the island has dwindled to only a small portion of its ancient size.
The wall itself stands about two meters tall and averages 20 meters across. Divers also located large granite monoliths at regular intervals, sticking up from the wall in two straight rows.
If the structure really was designed for trapping fish, the parallel lines of standing stones may have once held a net made from branches or sticks, that were used to catch fish as the tide moved out.
In total, the wall weighs roughly 3,300 tonnes. Because of its size, researchers think it must have been created by a sizeable and stable community.
It obviously also has a solid construction, seeing as how it has lasted 7,000 years.
Archaeologist Yvan Pailler explained that the wall was likely constructed by an organized group of hunter gatherers who settled in one place when conditions allowed.
He added that it could also have been built by early Neolithic groups that arrived in the region around 5,000 BC.
The structure was identified when geologist Yves Fouquet reviewed seafloor depth maps created with modern radar imaging.
Right off the coast of Sein, he spotted a 120-meter line cutting across an underwater valley, and he realized right away that it wasn’t natural.
Archaeologists tried to investigate the site in 2022, but heavy seaweed forced them to postpone the dive until the next winter.
In a paper published in the International Journal of Nautical Archaeology, scientists suggest that places like this submerged wall could be the source of old Breton stories about cities lost beneath the sea.
